1. Field of the Invention
This disclosure relates to a semiconductor device, and more particularly, to a fuse box of a semiconductor device and a fabrication method thereof.
2. Description of the Related Art
Semiconductor devices (chips) formed on a semiconductor substrate are electrically tested prior to an assembly process. As a result, the semiconductor devices may be classified as either “good” chips or “bad” chips. In the case where bad chips malfunction due to at least one bad cell, the bad cell can be replaced with a redundant cell by a repair process.
The repair process includes a step of cutting some fuses using laser beam irradiation such that the redundant cell has the address of the bad cell in a writing mode and a reading mode.
The fuses are generally formed of bit lines, which data is transmitted through, at the same time. Further, the bit lines are typically formed under metal lines. Particularly, a semiconductor device such as DRAM has cell capacitors interposed between the metal lines and the bit lines. Therefore, the total thickness of an interlayer insulating layer stacked on the upper part of the fuses may be greater than 1 μm.
FIG. 1A is a plan diagram showing a fuse box formed according to the conventional art.
Referring to FIG. 1A, a fuse box 60 includes several fuses 15 aligned in line, a guard ring 47 having a plate line 25 for defining the area of the fuse box 60, a contact hole 40 and an upper metal line 45, and a window 55 formed in the fuse box 60.
The fuse box 60 includes the window 55 for opening the fuses 15, which are formed at the central region of the fuse box 60. The window 55 allows the fuses 15 to be effectively cut by the laser beam. The plate line 25 is formed of a conductive layer.
However, as the integration density of semiconductor devices increase, the pitch of the fuses 15 gradually decrease. In this case, when a selected fuse in the fuse box 60 is cut by the laser beam, other fuses adjacent to the selected fuse may be damaged. To solve the above problem, the pitch of the fuse 15 should be increased.
To increase the pitch of the fuses 15, the area of the fuse box 60 containing the fuses 15 is increased, resulting in a decrease of the integration density in the semiconductor device.
FIGS. 1B to 1D are cross-sectional diagrams taken along the line I-I′ of FIG. 1A for illustrating a fabrication method of the conventional fuse box.
Referring to FIGS. 1B to 1C, a first insulating layer 10 is formed on a semiconductor substrate 5, and a plurality of fuses 15 are formed on predetermined regions of the first insulating layer 10 to be parallel with each other. The fuses 15 are typically formed of a conductive layer such as a tungsten polycide layer. Then, a second insulating layer 20 is formed on the whole surface of the semiconductor substrate having the fuses 15. Next, conductive layer patterns 25a, 25b are formed on the second insulating layer. The conductive layer patterns 25a, 25b are formed from the same doped polysilicon layer as the plate line of FIG. 1A, and are referred to as the first and the second conductive layer patterns, respectively.
A third and a fourth insulating layer 30, 35 are formed sequentially on the whole surface of the semiconductor substrate 5 having the conductive layer patterns 25a, 25b. And the third and fourth insulating layers 30, 35 are etched in sequence to form a contact hole 40, which exposes the top surface of the first conductive layer pattern 25a. Then, an upper metal line 45 is formed on the semiconductor substrate 5 having the contact hole 40. The upper metal line 45 buries the contact hole 40 and is formed on the top surface of the fourth insulating layer 35 to overlap the contact hole 40. At this time, the upper metal line 45 is electrically connected to the first conductive layer pattern 25a through the contact hole 40. The first conductive layer pattern 25a and the upper metal line 45 together with the contact hole 40 form a guard ring 47 as shown in FIG. 1A. A fifth insulating layer 50, such as a passivation layer, is formed on the whole surface of the semiconductor substrate 5 having the upper metal line 45. The fifth insulating layer 50 includes at least one layer. As a result, several insulating layers may be stacked on the fuses 15, making it increasingly difficult to cut the fuses 5 using the laser beam.
Referring to FIG. 1D, a window 55 is formed inside the guard ring 47 by sequentially etching the fifth insulating layer 50, the fourth insulating layer 35, the third insulating layer 30, the second conductive layer pattern 25b, and a portion of the second insulating layer 20. Accordingly, the remaining portion of the second insulating layer 20 has a predetermined thickness that is sufficient to partially absorb the energy applied to the fuses 15 by the laser beam. However, the thickness of the second insulating layer 20 covering the fuses 15 may be non-uniform throughout the whole surface of the semiconductor substrate 5. This is caused by a non-uniform etching ratio that occurs over the whole surface of the semiconductor substrate 5 during an etching process for forming the window 55.
In particular, the thicker the second to fifth insulating layers 20, 30, 35, 50 are, the less uniform the etching ratio becomes. It is generally difficult to make the thickness of the second insulating layer 20 remaining on the fuses 15 uniform over the whole surface of the semiconductor substrate 5. As a result, it is difficult to expect a successful repair process.
U.S. Application Publication No. 2002/0014680 to Isao Tottori discloses fuses in a semiconductor device and a method of manufacturing the same. According to 2002/0014680, a metal fuse formed inside a fuse box of the semiconductor device is connected to the source and drain regions of a gate formed on a semiconductor substrate. Thus, the metal fuse is formed of metal lines that are connected from the semiconductor substrate to the fuse being cut by the laser beam.
The metal lines are formed by the connection of tungsten (W) layers and aluminum (Al) layers, and the cutting of a metal fuse is done by using a current applied to the semiconductor device.
The use of current avoids both the attack of adjacent fuses from the conventional laser beam, and also the phenomenon where the metal fuse is not cut due to the non-uniform thickness of an insulating layer covering the fuses on predetermined regions of the semiconductor device.
Unfortunately, the above structure having the metal lines may increase the production cost of the semiconductor device by using at least one additional metal layer, and the direct contact of metals with the semiconductor substrate may increase the chances of metal contamination to the semiconductor device, causing the performance of the semiconductor device to deteriorate.
Embodiments of the invention address these and other disadvantages of the conventional art.